Plasma jets have been conventionally used to subject workpieces to surface treatment or processing such as cutting, etching, or film deposition and also used in various fields such as the high-temperature treatment of hazardous substances.
For such plasma jet uses, a known method using direct-current arc discharge is used to generate a fine plasma jet with a diameter of 2 mm or less. Such a method has various problems that electrodes are worn, reactive gas cannot be used, and workpieces are limited to conductors.
Microplasma jet generators have been recently attracting much attention because the microplasma jet generators can be used for practical applications such as plasma display panels (PDPs). Furthermore, it has been attempted to apply the microplasma jet generators to analyzers for chemical or biochemical analysis and process systems for processing or surface-treating microchips for use in micro-devices.
In the field of chemical or biochemical analysis in particular, a novel μTAS for performing high-throughput analysis is being intensively investigated. In the μTAS, the following system and method are used in combination: a flow analysis system that includes a silicon, glass, or plastic chip having micro-grooves with a width of several ten micrometers so as to isolate a trace amount of a substance at high speed by gas chromatography (GC) or micro-capillary electrophoresis (μCE) and an on-chip high-sensitivity detection method such as laser-induced fluorescence detection or electrochemical analysis using micro-electrodes. It is expected to use the μTAS for various applications such as gene analysis, medical examination, and pharmaceutical development.
For bench-top analyzers, the following method has been recently developed: a high-throughput, ultra high-sensitivity detection method using a separation technique such as capillary electrophoresis in combination with inductively coupled plasma optical emission spectroscopy (ICP-OES) or ICP mass spectroscopy that is a known technique for analyzing elements with extremely high sensitivity. Therefore, there is an idea that high-density microplasma is generated on a glass chip or another chip, which is incorporated in the μTAS, which is used for a high-sensitivity detection module.
A. Manz et al. reported the first microplasma chip for analysis in 1999, the chip being incorporated in a μTAS for detecting an atom or a molecule by GC (gas chromatography). They generated a helium DC glow discharge in a microspace, formed in a glass chip, having a width of 450 μm, a depth of 200 μm, and a length of 2000 μm at a pressure of about 17 kPa with an electric power of 10 to 50 mW and estimated the detection limit of methane to be 600 ppm. Since a cathode was sputtered under such vacuum conditions, the discharge was discontinued within two hours. Thereafter, they reported that the discharge was continued for 24 hours at atmospheric pressure.
The first reported microplasma chip, equipped with no electrode, operating at atmospheric pressure is a 2.45 GHz microwave discharge chip including a micro strip antenna. In the discharge chip, a discharge with a length of 2 to 3 cm is generated in a discharge chamber having a depth of 0.9 mm, a width of 1 mm, and a length of 90 mm with a power of 10 to 40 W and the detection limit of mercury vapor is 10 ng/ml.
Since it is difficult to stably generate high-density plasma in a microspace with a small electric power, it has been considered to be impossible to perform high-resolution microanalysis by generating microplasma in a μTAS chip.
In such circumstances, the inventor has proposed a μTAS using a VHF-driven inductively-coupled microplasma source and succeeded in developing high-resolution microanalysis (Patent Document 1). With reference to FIG. 10, the VHF-driven inductively-coupled microplasma source disclosed in Patent Document 1 is a microplasma chip 110 including a discharge tube 103 disposed in a center region of a 30 mm square substrate 101 made of quartz and a one-turn flat antenna 102. The microplasma chip 110 is driven with a VHF power supply. A plasma gas 104 is introduced into one end of the discharge tube 103 and a microplasma jet 105 is discharged from the other end.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-257785 (Claims, FIG. 1, and so on).